Refer to the fishery data in Example 12.17.
a. Fit a second- order model relating catch to residency, size, and structure (with the squared terms but without the cross- product terms) with separate intercepts and slopes for those lakes with access and those without access (access is used as an indicator variable).
b. Display the fitted regression lines for lakes both with and without access.
c. Test whether the squared terms in residency, size, and structure provide a significant improvement to the fit of the model compared to the model with just the first- order terms.